
<!DOCTYPE html>
<html>
  <head>
    <script src="https://unpkg.com/konva@4.0.18/konva.min.js"></script>
    <meta charset="utf-8" />
    <title>Konva Zoom Relative to Stage Demo</title>
    <style>
      body {
        margin: 0;
        padding: 0;
        overflow: hidden;
        background-color: #f0f0f0;
      }
    </style>
  </head>

  <body>
    <div id="container"></div>
    <script>
      var width = window.innerWidth;
      var height = window.innerHeight;

      var stage = new Konva.Stage({
        container: 'container',
        width: width,
        height: height
      });

      var layer = new Konva.Layer();
      stage.add(layer);

      var circle = new Konva.Circle({
        x: stage.width() / 2,
        y: stage.height() / 2,
        radius: 50,
        fill: 'green'
      });
      layer.add(circle);

      layer.draw();

      var scaleBy = 1.01;
      stage.on('wheel', e => {
        e.evt.preventDefault();
        var oldScale = stage.scaleX();

        var mousePointTo = {
          x: stage.getPointerPosition().x / oldScale - stage.x() / oldScale,
          y: stage.getPointerPosition().y / oldScale - stage.y() / oldScale
        };

        var newScale =
          e.evt.deltaY > 0 ? oldScale * scaleBy : oldScale / scaleBy;
        stage.scale({ x: newScale, y: newScale });

        var newPos = {
          x:
            -(mousePointTo.x - stage.getPointerPosition().x / newScale) *
            newScale,
          y:
            -(mousePointTo.y - stage.getPointerPosition().y / newScale) *
            newScale
        };
        stage.position(newPos);
        stage.batchDraw();
      });
    </script>
  </body>
</html>